Yes, you can do this live. You can even change the compression type...

Remember the distinction between zfs pools and filesystems. Compression properties are set at the zfs filesystem level.

New data to the pool will be uncompressed if you turn it off.

May I ask why you're interested in disabling compression? The recommendation for ZFS is to leave compression ON unless you know your dataset if going to be comprised of non-compressible data (e.g. .tiff files or other media files).